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Babesiosis is an infection that damages the red blood cells. Red blood cells travel in the blood and carry oxygen throughout the body. Damage to a large number of these cells can decrease the level of oxygen in the blood.

Mild babesiosis may not cause symptoms. Severe illness can lead to serious and life threatening problems because of the destruction of red blood cells.


Babesiosis is caused by a Babesia parasite. It is most often passed to humans through a bite from an infected tick.

Rarely, the parasite can be passed through a blood transfusion from an infected donor.

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A Tick

Risk Factors

Spending time in an area where ticks are common increases your risk of infection. This includes outdoor areas with high grass or bushes. Not all tick bites will lead to infections.

The risk of a severe infection is increased in certain people including:

  • Elderly
  • People with weak immune systems, such as those with HIV or cancer
  • People with liver disease
  • People with kidney disease
  • People who have had a spleen removal or have a spleen that does not work properly

Common geographic locations include:

  • North America—Northeast, upper Midwest, northern areas along the Pacific coast
  • Europe—British Isles and other locations across continental Europe
  • Parts of Asia, Africa, and South America

The risk of tick bites is highest from May to October.


Many people will have no symptoms. Symptoms that do develop may not show up until a few days or weeks after the bite. They are often flu-like symptoms such as:

  • Fever
  • Chills
  • Sweating
  • Muscle and joint aches
  • Nausea and loss of appetite
  • Headaches
  • Fatigue

A severe infection can cause difficulty breathing. It can also lead to complications with the heart, liver, or kidney.


You will be asked about your symptoms and medical history. You may be asked if you have spent time in areas known for ticks. A physical exam will be done.

The ticks that spread this infection tend to be very small. You may not have known you were bitten.

A blood test can confirm the presence of the infection and any other infection that may have been passed from the tick such as Lyme disease, ehrlichiosis, or anaplasmosis. Blood tests may also be done to look for damage to other organs such as the kidneys or liver.


Infections without symptoms usually do not require treatment. Your immune system is able to clear the parasite.

An infection that causes symptoms may be treated with a combination of antibiotic and antiparasitic medications.

Severe infections can lead to very low levels of red blood cells. This is a condition known as hemolytic anemia. This may require a hospital stay, blood transfusions, and other supportive care until the infection can be cleared.

With this infection, it may be some time before the parasite is completely cleared.

Do not donate blood until your doctor has said it is okay to do so. If you donated blood just before your diagnosis, let your doctor know.


Avoiding tick bites is the best way to avoid babesiosis. Learn when ticks are most active in your area. Avoid tall grass, woods, and brush during these times. If you are in these areas:

  • Wear light colored clothing to make ticks easier to see.
  • Wear long pants and socks. Consider tucking your pants into your socks so the ticks have a harder time getting to your skin.
  • Use a bug repellant that contains DEET. Use as directed on the container.

After being outdoors:

  • Check yourself and your pets thoroughly for ticks.
  • If a tick is attached to the skin, remove it as soon as possible. Grab the tick close to your skin and pull out with steady pressure. Wash the area where the tick was attached with soap and water.

It may take at least 24 hours for the parasite to pass through the bite. Not all tick bites will cause an infection. If you were bitten by a tick, watch the area over the next few days. Call your doctor if you develop a rash or other symptoms.

Revision Information

  • Centers for Disease Control and Prevention

  • Family Doctor—American Academy of Family Physicians

  • Healthy Canadians

  • Public Health Agency of Canada

  • Babesiosis. Centers for Disease Control and Prevention (CDC) website. Available at: Updated July 10, 2012. Updated July 10, 2012. Accessed September 3, 2015.

  • Babesiosis. EBSCO DynaMed website. Available at: Updated June 23, 2014. Accessed September 3, 2015.

  • Babesiosis FAQs. National Institute of Allergy and Infectious Diseases website. Available at: Updated April 10, 2014. Accessed September 3, 2015.

  • Mylonakis E. When to suspect and how to monitor babesiosis. Am Fam Physician. 2001;63(10):1969-1975.